The patent is for a reinforced concrete structure that makes up a composite having many longitudinally oriented fibers embedded in a matrix of a depolymerizable and repolymerizable rigid thermoplastic polyurethane resin. This resin has a glass transition temperature (Tg) of at least 50° C. and a hard segment content (defined as the proportion of the weight of the TPU that is made up of chain extender and polyisocyanate residues) of at least 75 percen, The composite has the longest cross-sectional dimension of not more than 5 mm and an aspect ratio of at least 10, and is then embedded in concrete to reinforce the it.